Selenazolinocarbocyanine dye and process of preparing it



Patented May 8, 1934 UNETED STATES PATENT FFICE SELENAZOLINOCARBOCYANINEDYE AND PROCESS OF PREPARING IT No Drawing. Application September 21,1931, Serial No. 564,138

14 Claims. (01. 260-44) This invention relates to a new composition ofmatter and particularly to a new class of dyes, useful for sensitizingphotographic emulsions, and to methods for preparing those dyes and thebase from which the dyes originate.

As ordinary photographic emulsions are generally indifferent to thosecolors of the spectrum of longer wave lengths, various types ofsensitizing dyes have been suggested for incorporation in photographicemulsions or for employing over emulsions as overcoatings, so as toincrease the spectral sensitiveness thereof. The new dyes describedherein depart from the class of most of those previously suggested inthat they contain selenium in the nuclei which are condensed to form thedye.

An object of the present invention is to provide a process for thepreparation of dyes of the selenazolinocarbocyanine series containingselenazoline nuclei, joined by a three carbon chain; the hydrogen of thecentral carbon atom of which may or may not be substituted. A furtherobject of this invention is to provide such dyes as may be added tophotographic emulsions, such as gelatino-silver-halide emulsions, orcoated thereon as an overcoating whereby the spectral sensitivity of thephotographic emulsion is increased. A further object of this inventionis to provide a process for preparing the Z-methylselenazoline base andits quaternary salts. Other objects will hereinafter appear.

I have discovered that the new base which is termed Z-methylselenazoline(after analogy to 2-methylthiazoline) gives rise to a new class of dyeswhich I prepare by the condensation of an alkyl quaternary salt of thebase with an orthoester of a monobasic carboxylic acid. The reaction maybe advantageously carried out in boiling dry pyridine. The ortho-estersof the carboxylic acids which I have found particularly suitable includeas ortho-esters of the aliphatic carboxylic acids, such ortho-esters as,trimethyl or triethyl orthoformate, acetate, propionate caproate,valerate and the like; as ortho-esters of the substituted aliphaticcarboxylic acids, such esters as trimethyl or triethylortho-gamma-phenoxybutyrate and trimethyl or triethylorthophenylacetate; and as ortho-esters of aromatic carboxylic acidssuch esters as trimethyl or triethyl orthobenzoate and trimethyl ortriethyl ortho-ptoluate. Ortho-esters of substituted aromatic carboxylicacids may also be employed, such for example as where the aryl group(phenyl) is substituted by an alkyl group (methyl) or the like.

The trimethyl and triethyl ortho-esters are illustrative and are not tobe understood as limiting my invention to their use only. Instead ofusing trimethyl or triethyl orthoacetate I may employ methyldiethyl ordimethylethyl orthoacetate; instead of trimethyl or triethylorthopropionate one 39 may employ dimethylethyl or ethyl-di-n-propylorthopropionate and insteadof using trimethyl or triethylortho-n-caproate I may use methyldiethyl ortho-n-caproate, etc. In otherwords the alkoxy groups of the ortho-ester may be dis- 5 similar, ifdesired, since the dye obtained will have the same structural formulaWhether the alkoxy groups are the same or diiferent.

2-Methylselenazoline has the following structural formula:

1 H2C5 H 5 /2COH;

Z-Methylselenazoline may be prepared, I have found, as follows:

10.8 g. (1 mol.) of c-bromoethylamine hydrobromide are heated in a smallround-bottomed 30 flask on a steam bath. To this hot p-bromoethylaminehydrobromide there is added in small portions, over a period of aboutthree minutes while it is stirred with a glass rod 6.5 g. (1 mol.) offreshly prepared selenoacetamide. A melt is 5 formed before all theselenoacetamide is added. The heating is continued for about fiveminutes, during which time the reaction mixture sets solid in the flask;this solid is dissolved in 200 cc. water, made alkaline by the additionof 40%sodium 9Q hydroxide and the Z-methyl-selenazoline thus liberateddistilled from this alkaline solution by steam distillation. About 50cc. distillate iscollected. Some of the Z-methylselenazoline separatesas an oil and remains as the bottom layer. This layer is separated bymeans of a separatory funnel. The aqueous layer is then treated withpulverized potassium hydroxide whereupon more Z-methylselenazolineseparates out, which is collooted by extraction with ethyl ether. Thisether extract is added to the 2-methylselenazoline which has previouslybeen removed from the distillate at the separatory funnel and the Wholeis then dried with solid potassium carbonate. After decanting theanhydrous ethyl ether layer (containing the 2-methylselenazoline) fromthe potassium carbonate, the ether is then distilled off leavingZ-methylselenazoline as a residue which may be further purified bydistilling under reduced pressure. The 2-methylselenazoline distills asa colorless liquid boiling at 71-72 C. at 35 mm. pressure of mercury.

When this 2-Inethylselenaz0line is acted upon by a compound having asuitable acid radical such as methyl or ethyl iodide, there is producedthe Z-methylselenazoline alkyl quaternary salt having the followingstructural formula for the methiodide:

Se Hzo H 4 20-0113 2 \g/ Ca \I The ethiodide has an identical formulaexcept that an ethyl group replaces the methyl group shown attached tothe nitrogen. It will thus be noted that I employ a base which has areactive methyl group in the 2-position.

When two molecular proportions of this 2- methylselenazoline al'kylquaternary salt are condensed in the presence of dry pyridine, forinstance, with 1 molecular proportion of an orthoester of a monobasiccarboxylic acid, such as those described above, for instance, ethylorthoforinate, there occurs the following probable reaction:

Se Sc resulting in the formation of the dye shown. If a dye substitutedin the 7-position is desired, one employs the proper ortho-ester, forinstance, if one desired to have an ethyl group substituted for thehydrogen in the 7-position, one employs the ortho-ester of propionicacid. The reaction which occurs when for instance, triethyl orthoacetateor propionate is employed, is analogous to the reaction when ethylorthoiormate is employed and may be represented by the followingreaction:

It will be noted from the above reactions that the dye formed has thesame structural formula whether R and R are the same or dissimilar.

While the above reaction represents the formation of one of thepreferred types of dyes, it is possible, as indicated above, to employsome other alkyl quaternary salt and thereby form a dye which has in theposition X, an acid radical which it is desirable to replace by a moresuitable acid radical. Thus, if I were to employ 2-rnethylselenazolinemethosulphate or Z-methylselenazoline methop-toluenesulfonate as thealkyl quaternary salt, I would obtain respectively, the methosulphate ormetho-p-toluenesulfonate of the dye; by then treating either or'both ofthese in solution with an aqueous solution of a salt containing asuitable acid radical I may convert the dye to a salt, other than thesalt of formation; for instance, if I wished the iodide of the dye Iwould treat either the methosulphate, metho p toluenesulfonate or bothin solution with an aqueous solution of potassium iodide.

In the above structural formula R, R and R represent alkyl groups suchfor instance as methyl or ethyl and X a suitable acid radical as beforeindicated.

As before pointed out, if I employ an orthoester of a carboXylic acidhaving more than one carbon atom there would result a dye in which Arepresents the substituent group introduced into the three carbon chainconnecting the nuclei. This three carbon chain consists of threemethenyl groups linked together as a trimethenyl chain having thestructural formula:

This chain links together the selenazoline nuclei. The substituted groupA replaces the hydrogen of the central carbon atom of this trimethenylchain.

The nomenclature and numbering of the above groups of compounds andintermediates are analogous to the usage and system of numberingemployed in connection with the known thiazolinocaroocyanines. Thenumbering, of course, is arbitrary and is given for the guidance ofthose skilled in the art in order that there be no question as to theidentity of the compounds covered by invention.

The following examples are typical of the manner in which my inventionmay be carried out, although it will be understood that these examplesare intended to be merely illustrative and not to limit my invention inany way.

Eicample 1 3:3-Diethylselenazolinoearbocyanine iodide. 3 g. (2 mole.) ofZ-methylselenazoline were heated on a steam bath under reflux forseveral hours (for instance four hours) with 4.7 g. (2 mols.+5ii%excess) of ethyl iodide. At the end of this period, during which thealkyl quaternary salt was formed, the condenser was disconnected and theexcess of ethyl iodide allowed to evaporate. The dark alkyl quaternarysalt was washed with three separate portions of acetone. After the lastwashing the last traces of acetone were removed by heating on the steambath, care being taken to keep out as much moisture as possible. To thiscrude alkyl quaternary salt was added 25 cc. of dry pyridine and 3 co.(in excess of 1 mol.) of ethyl orthoformate. This was quickly brought toa boil over a free flame under reflux with shaking and boiled gently fora period of time, such for instance as 45 minutes. Upon cooling (afreezing mixture may be used to advantage) crystals separated from thisreaction mixture. The addition of acetone was found to increase theamount of crystals which separate.

These crystals were then. collected on a filter,

washed with water followed by acetone, and dried. They were thenrecrystallized from methyl alcohol. When the solution is quite cold itwill be found advantageous to add a small amount of acetone to aid thecrystallization'of this dye. Crystals were collected on the filter,washed with acetone and dried. These crystals are orange color and adilute methyl alcohol solution thereof has a bright yellow coloration.

Example 2 3 3'- Dimethyl 7 ethylselenazolinocarbocyanine iodide 1.85 g.(2 mols.) of Z-methylselenazoline were heated on a steam bath for a fewhours, for instance three hours, under reflux with 2.9 g. (2 mols.+60%excess) of methyl iodide. The reflux condenser was removed and theexcess methyl iodide allowed to evaporate in the air. This crude alkylquaternary salt was treated with 10 cc. of dry pyridine and 3 cc. (inexcess of 1 mol.) of trimethyl orthopropionate. This was quickly broughtto a boil over a free flame and gentle boiling continued for a period oftime, for instance 45 minutes. Crystals separated from this reactionmixture after being cooled under refrigeration. These crystals werecollected on a filter, washed and dried, then recrystallized from methylalcohol. The addition of a small amount of acetone to the cold alcoholicsolution gives a further precipitation of crystals of the dye. Thesewere collected on a filter, washed with acetone and dried. Likewisethese crystals are orange color; a dilute alcoholic solution thereof hasa bright yellow coloration.

As indicated in the earlier portion of this specification, I may,instead of employing triethyl orthoformate or trimethyl orthopropionate,employ any of the ortho-esters of carboxylic acids set forth above orones similar thereto. Thus, when ethyl orthoformate is employed, it willbe apparent that I obtain a dye unsubstituted in the '7-position, whilewith ortho-esters, the acid of which contains more than one carbon atom,I can obtain at will a dye in which there is substituted in the'7-position of the trimethenyl chain, either an alkyl group, asubstituted alkyl group or an aryl or substituted aryl group. Thus, theletter A in the above structural formula indicates any of thesegroupings. As before indicated various alkyl groups may be employed inthe portion indicated by the letter R to obtain different dyes ofvarying properties. The character X in the above formulae indicates anysuitable acid radical such as a halide, p-toluene-sulfonate,alkylosulphate, nitrate, acetate, perchlorate or the like.

While the principal use now known for these new chemical compounds isfor sensitizing photographic emulsions it may well be that other usestherefore will be discovered from time to time and consequently it isnot intended that the foregoing description of the sensitizingproperties of these dyes shall in any way limit the scope of the claimsappended hereto.

What I claim as my invention and desire to secure by Letters Patent ofthe United States is:

1. A carbocyanine dye of the following structure So So in which R equalsalkyl, X equals an acid radical and A equals hydrogen, an alkyl group oran aryl group of the benzene series.

2. A carbocyanine dye of the following structure H.C f3...

and A equals an alkyl group.

3. A 3:3'-dialkylselenazolinocarbocyanine salt.

4. A 3:3 dimethylselenazolinocarbocyanine salt.

5. A 3:3 dimethylselenazolinocarbocyanine iodide.

6. A 3:3-diethylselenazolinocarbocyanine salt.

'7. A 3I3-diethylselenazolinocarbocyanine iodine.

8. A 3 :3 :7-trialkylselenazolinocarbocyanine salt.

9. A process for the preparation of selenazolinocarbocyanine salts whichcomprises condensing, under the influence of heat, two molecularproportions of a 2-methyl selenazoline alkyl quaternary salt with onemolecular proportion of an ortho ester of a monobasic carboxylic acid ofthe aliphatic or benzene series in the presence of an organic base whichis a solvent for the reactants and which acts to bind acid eliminatedfrom the quaternary salt as a result of the condensation.

10. A process for the preparation of selenazolinocarbocyanine saltswhich comprises condensing, under the influence of heat, two molecularproportions of a 2-methyl selenazoline alkyl quaternary salt with onemolecular proportion of an ortho ester of an aliphatic carboxylic acidin the presence of an organic base which is a solvent for the reactantsand which acts to bind acid eliminated from the quaternary salt as aresult of the condensation.

11. A process for the preparation of selenazolinocarbocyanine saltswhich comprises condensing, under the influence of heat, two molecularproportions of a Z-methyl selenazoline alkyl quaternary salt with onemolecular proportion of ethyl ortho formate in the presence of anorganic base which is a solvent for the reactants and which acts to bindacid eliminated from the quaternary salt as a result of thecondensation.

12. A process for the preparation of selenazolinocarbocyanine saltswhich comprises condensing, under the influence of heat, two molecularproportions of a Z-methyl selenazoline alkyl quaternary salt with onemolecular proportion of an ortho ester of a monobasic carboxylic acid ofthe aliphatic or benzene series in the presence of pyridine.

13. A process for the preparation of selenazolinocarbocyanine saltswhich comprises condensing, under the influence of heat, two molecularproportions of a 2-methyl selenazoline alkyl quaternary salt with onemolecular proportion of an ortho ester of an aliphatic carboxylic acidin the presence of pyridine.

14. A process for the preparation of selenazolinocarbocyanine saltswhich comprises condensing, under the influence of heat, two molecularproportions of a Z-methyl selenazoline alkyl quaternary salt with onemolecular proportion of ethyl ortho formate in the presence of pyridine.

FRANK L. WHITE.

